Apparatus for electrosurgical spine surgery

ABSTRACT

The present invention provides systems and methods for selectively applying electrical energy to a target location within of a patient&#39;s body, particularly including tissue in the spine. The present invention applies high frequency (RF) electrical energy to one or more electrode terminals in the presence of electrically conductive fluid to remove, contract or otherwise modify the structure of tissue structures. In one aspect of the invention, a method is provided for treating herniated discs within a patient&#39;s spine by applying sufficient electrical energy to the disc tissue to reduce a volume of the disc, thereby relieving pressure on a spinal nerve. In one embodiment, the high frequency voltage is sufficient to ablate a portion of the nucleus pulposis, either the extruded portion outside of the annulus or a portion or all of the pulposis within the annulus. In another embodiment, the electrode terminal is advanced into the annulus and sufficient high frequency voltage is applied to contract or shrink the collagen fibers within the nucleus pulposis. This causes the pulposis to shrink and withdraw from its impingement on the spinal nerve.

RELATED APPLICATIONS

This is a division of and claims the benefit of U.S. application Ser.No. 09/026,851/Feb. 20, 1998 which is a continuation-in-part of Ser. No.08/690,159/Jul. 18, 1996 now U.S. Pat. No. 5,902,272 and acontinuation-n-part of Ser. No. 08/942,580/Oct. 2, 1997 now U.S. Pat.No. 6,159,194 the disclosure of which is incorporated by reference.

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/690,159, filed Jul. 18, 1996, the complete disclosure ofwhich is incorporated herein by reference for all purposes. Thisapplication also derives priority from U.S. patent application No.08/942,580 entitled “Systems and Methods for Electrosurgical TissueContraction”, filed on Oct. 2, 1997 and U.S. Patent Application entitled“Systems and Methods for Endoscopic Sinus Surgery”, filed on Dec. 15,1997, the complete disclosures of which are incorporated herein byreference for all purposes.

The present invention is related to commonly assigned co-pendingProvisional Patent Application Nos. 601062,996 and 60/062,997,non-provisional U.S. patent application Ser. No. 08/970,239 entitled“Electrosurgical Systems and Methods for Treating the Spine”, filed Nov.14, 1997, and 08/977,845 entitled “Systems and Methods forElectrosurgical Dermatological Treatment”, filed on Nov. 25, 1997, U.S.application Ser. No. 08/753,227, filed on Nov. 22, 1996, and PCTInternational Application, U.S. National Phase Ser. No. PCT/US94/05168,filed on May 10, 1994, now U.S. Pat. No. 5,697,281, which was acontinuation-in-part of application Ser. No. 08/059,681, filed on May10, 1993, which was a continuation-in-part of application Ser. No.07/958,977, filed on Oct. 9, 1992 which was a continuation-in-part ofapplication Ser. No. 07/817,575, filed on Jan. 7, 1992, the completedisclosures of which are incorporated herein by reference for allpurposes. The present invention is also related to commonly assignedU.S. Pat. No. 5,683,366, filed Nov. 22, 1995, and U.S. Pat. No.5,697,536, filed on Jun. 2, 1995, the complete disclosures of which areincorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly to surgical devices and methods which employ highfrequency electrical energy to treat tissue in regions of the spine. Thepresent invention is particularly suited for the treatment of herniateddiscs.

The major causes of persistent, often disabling, back pain aredisruption of the disc annulus, chronic inflammation of the disc (e.g.,herniation), or relative instability of the vertebral bodies surroundinga given disc, such as the instability that often occurs due to adegenerative disease. Spinal discs mainly function to cushion and tetherthe vertebrae, providing flexibility and stability to the patient'sspine. Spinal discs comprise a central hydrostatic cushion, the nucleuspulposus, surrounded by a multi-layered ligament, the annulus fibrosis.As discs degenerate, they lose their water content and height, bringvertebrae closer together. This results in a weakening of the shockabsorption properties of the disc and a narrowing of the nerve openingsin the sides of the spine which may pinch your nerve. This discdegeneration can eventually cause back and leg pain. Weakness in theannulus from degenerative discs or disc injury can allow fragments ofnucleus pulposis from within the disc space to migrate into the spinalcanal. There, displaced nucleus or protrusion of annulus fibrosis, e.g.,herniation, may impinge on spinal nerves. The mere proximity of thenucleus pulposis or a damaged annulus to a nerve can cause directpressure against the nerve, resulting in numbness and weakness of legmuscles.

Often, inflammation from disc herniation can be treated successfully bynon-surgical means, such as rest, therapeutic exercise, oralanti-inflammatory medications or epidural injection of corticosteroids.In some cases, the disc tissue is irreparably damaged, therebynecessitating removal of a portion of the disc or the entire disc toeliminate the source of inflammation and pressure. In more severe cases,the adjacent vertebral bodies must be stabilized following excision ofthe disc material to avoid recurrence of the disabling back pain. Oneapproach to stabilizing the vertebrae, termed spinal fusion, is toinsert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted from other portions of the body, such as the hip, and packedinto the implants. This allows the bone to grow through and around theimplant, fusing the vertebral bodies and alleviating the pain.

Until recently, spinal discectomy and fusion procedures resulted inmajor operations and traumatic dissection of muscle and bone removal orbone fusion. To overcome the disadvantages of traditional traumaticspine surgery, minimally invasive spine surgery was developed. Inendoscopic spinal procedures, the spinal canal is not violated andtherefore epidural bleeding with ensuring scarring is minimized orcompletely avoided. In addition, the of instability from ligament andbone removal is generally lower in endoscopic procedures than with opendiscectomy. Further, more rapid rehabilitation facilitates fasterrecovery and return to work.

Minimally invasive techniques for the treatment of spinal diseases ordisorders include chemonucleolysis, laser techniques and mechanicaltechniques. These procedures generally require the surgeon to form apassage or operating corridor from the external surface of the patientto the spinal disc(s) for passage of surgical instruments, implants andthe like. Typically, the formation of this operating corridor requiresthe removal of soft tissue, muscle or other types of tissue depending onthe procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back,etc.). This tissue is usually removed with mechanical instruments, suchas pituitary rongeurs, curettes, graspers, cutters, drills,microdebriders and the like. Unfortunately, these mechanical instrumentsgreatly lengthen and increase the complexity of the procedure. Inaddition, these instruments sever blood vessels within this tissue,usually causing profuse bleeding that obstructs the surgeon's view ofthe target site.

Once the operating corridor is established, the nerve root is retractedand a portion or all of the disc is removed with mechanical instruments,such as a pituitary rongeur. In addition to the above problems withmechanical instruments, there are serious concerns because theseinstruments are not precise, and it is often difficult, during theprocedure, to differentiate between the target disc tissue, and otherstructures within the spine, such as bone, cartilage, ligaments, nervesand non-target tissue. Thus, the surgeon must be extremely careful tominimize damage to the cartilage and bone within the spine, and to avoiddamaging nerves, such as the spinal nerves and the dura matersurrounding the spinal cord.

Lasers were initially considered ideal for spine surgery because lasersablate or vaporize tissue with heat, which also acts to cauterize andseal the small blood vessels in the tissue. Unfortunately, lasers areboth expensive and somewhat tedious to use in these procedures. Anotherdisadvantage with lasers is the difficulty in judging the depth oftissue ablation. Since the surgeon generally points and shoots the laserwithout contacting the tissue, he or she does not receive any tactilefeedback to judge how deeply the laser is cutting. Because healthytissue, bones, ligaments and spinal nerves often lie within closeproximity of the spinal disc, it is essential to maintain a minimumdepth of tissue damage, which cannot always be ensured with a laser.

Monopolar radiofrequency devices have been used in limited roles inspine surgery, such as to cauterize severed vessels to improvevisualization. These monopolar devices, however, suffer from thedisadvantage that the electric current will flow through undefined pathsin the patient's body, thereby increasing the risk of unwantedelectrical stimulation to portions of the patient's body. In addition,since the defined path through the patient's body has a relatively highimpedance (because of the large distance or resistivity of the patient'sbody), large voltage differences must typically be applied between thereturn and active electrodes in order to generate a current suitable forablation or cutting of the target tissue. This current, however, mayinadvertently fl ow along body paths having less impedance than thedefined electrical path, which will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingsurrounding tissue or neighboring peripheral nerves.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures within a patient'sbody, such as tissue within or around the spine. The systems and methodsof the present invention are particularly useful for ablation,resection, aspiration, collagen shrinkage and/or hemostasis of tissueand other body structures in open and endoscopic spine surgery.

In one aspect of the invention, a method is provided for treatingherniated discs within a patient's spine. Specifically, the method ofthe present invention comprises introducing an electrosurgical probewithin the spine (either endoscopically, or through an open procedure)so that one or more electrode terminal(s) are brought into at leastpartial contact or close proximity with the target herniated disc. Highfrequency voltage is then applied between the electrode terminal(s) andone or more return electrode(s) to apply sufficient energy to the disctissue to reduce a volume of the disc, thereby relieving pressure on aspinal nerve. In one embodiment, the high frequency voltage issufficient to ablate a portion of the nucleus pulposis, either theextruded portion outside of the annulus or a portion or all of thepulposis within the annulus. In another embodiment, the electrodeterminal is advanced into the annulus and sufficient high frequencyvoltage is applied to contract or shrink the collagen fibers within thenucleus pulposis. This causes the pulposis to shrink and withdraw fromits impingement on the spinal nerve. In other embodiments, the presentinvention may be used to both ablate the extruded portion of the nucleuspulposis, and then to contract or shrink the inner disc material toallow repair of the annulus.

In a specific configuration, electrically conducting fluid, such asisotonic saline, is directed to the target site between the target disctissue and the electrode terminal. In monopolar embodiments, theconductive fluid need only be sufficient to surround the electrodeterminal, and to provide a layer of fluid between the terminal and thetissue. In bipolar embodiments, the conductive fluid preferablygenerates a current flow path between the electrode terminal(s) and oneor more return electrode(s).

In procedures requiring contraction of tissue, high frequency voltage isapplied to the electrode terminal(s) to elevate the temperature ofcollagen fibers within the tissue at the target site from bodytemperature (about 37° C.) to a tissue temperature in the range of about45° C. to 90° C., usually about 60° C. to 70° C., to substantiallyirreversibly contract these collagen fibers. In a preferred embodiment,an electrically conducting fluid is provided between the electrodeterminal(s) and one or more return electrode(s) positioned proximal tothe electrode terminal(s) to provide a current flow path from theelectrode terminal(s) away from the tissue to the return electrode (s).The current flow path may be generated by directing an electricallyconducting fluid along a fluid path past the return electrode and to thetarget site, or by locating a viscous electrically conducting fluid,such as a gel, at the target site, and submersing the electrodeterminal(s) and the return electrode(s) within the conductive gel. Thecollagen fibers may be heated either by passing the electric currentthrough the tissue to a selected depth before the current returns to thereturn electrode(s) and/or by heating the electrically conducting fluidand generating a jet or plume of heated fluid, which is directed towardsthe target tissue. In the latter embodiment, the electric current maynot pass into the tissue at all. In both embodiments, the heated fluidand/or the electric current elevates the temperature of the collagensufficiently to cause hydrothermal shrinkage of the collagen fibers.

In procedures requiring ablation of tissue, the tissue is removed bymolecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the electrodeterminal(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel or saline) between the electrode terminal(s) and the tissue.Within the vaporized fluid, a ionized plasma is formed and chargedparticles (e.g., electrons) are accelerated towards the tissue to causethe molecular breakdown or disintegration of several cell layers of thetissue. This molecular dissociation is accompanied by the volumetricremoval of the tissue. The short range of the accelerated chargedparticles within the plasma layer confines the molecular dissociationprocess to the surface layer to minimize damage and necrosis to theunderlying tissue. This process can be precisely controlled to effectthe volumetric removal of tissue as thin as 10 to 150 microns withminimal heating of, or damage to, surrounding or underlying tissuestructures. A more complete description of this phenomena is describedin commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure ofwhich is incorporated herein by reference.

In another aspect of the invention, the present invention is useful forhelping to create an operating corridor or passage between apercutaneous penetration in the patient's outer skin and a target areawithin the spine. Typically, th perating corridor is initially createdby inserting one or more dilators through the percutaneous penetrationto the target area within the spine, and then introducing a tubularretractor or similar instrument over the largest dilator. Once this isaccomplished, the hollow interior of the retractor (which will serve asthe operating corridor for the introduction of the necessaryinstruments, such as the endoscope) is typically partially filled withsoft tissue, muscle and other body structures. The present invention isparticularly useful for precisely and quickly removing these bodystructures to clear the operating corridor. To that end, anelectrosurgical probe according to the invention is delivered into thehollow retractor, and one or more electrode terminal(s) are positionedadjacent to or in contact with the soft tissue or other body structuresto be removed. High frequency voltage is applied between the electrodeterminal(s) and one or more return electrodes such that the tissue isremoved.

The tissue may be completely ablated in situ with the mechanismsdescribed above, or the tissue may be partially ablated and partiallyresected and aspirated from this operating corridor. In the latterembodiment, the method of the present invention further comprisesaspirating tissue fragments and fluid through an aspiration lumen in theelectrosurgical instrument or another instrument. In a preferredconfiguration, the probe will include one or more aspirationelectrode(s) at or near the distal opening of the aspiration lumen. Inthis embodiment, high frequency voltage is applied between theaspiration electrode(s) and one or more return electrode(s) (which canbe the same or different electrodes from the ones used to ablate tissue)to partially or completely ablate the tissue fragments as they areaspirated into the lumen, thus inhibiting clogging of the lumen andexpediting the tissue removal process.

The present invention offers a number of advantages over currentmechanical and laser techniques for spine surgery. The ability toprecisely control the volumetric removal of tissue results in a field oftissue ablation or removal that is very defined, consistent andpredictable. The shallow depth of tissue heating also helps to minimizeor completely eliminate damage to healthy tissue structures, cartilage,bone and/or spinal nerves that are often adjacent the target tissue. Inaddition, small blood vessels within the tissue are simultaneouslycauterized and sealed as the tissue is removed to continuously maintainhemostasis during the procedure. This increases the surgeon's field ofview, and shortens the length of the procedure. Moreover, since thepresent invention allows for the use of electrically conductive fluid(contrary to prior art bipolar and monopolar electrosurgery techniques),isotonic saline may be used during the procedure. Saline is thepreferred medium for irrigation because it has the same concentration asthe body's fluids and, therefore, is not absorbed into the body as muchas other fluids.

Apparatus according to the present invention generally include anelectrosurgical probe or catheter having a shaft with proximal anddistal ends, one or more electrode terminal(s) at the distal end and oneor more connectors coupling the electrode terminal(s) to a source ofhigh frequency electrical energy. For endoscopic spine surgery, theshaft will have a distal end portion sized to fit between adjacentvertebrae in the patient's spine. In some embodiments, the distal endportion is substantially planar, and it offers a low profile, to allowaccess to confined spaces without risking iatrogenic injury tosurrounding body structures or nerves, such as vertebrae or spinalnerves. Usually, the distal end portion will have a combined height(i.e., including the active electrode(s)) of less than 2 mm andpreferably less than 1 mm.

The apparatus will preferably further include a fluid delivery elementfor delivering electrically conducting fluid to the electrodeterminal(s) and the target site. The fluid delivery element may belocated on the probe, e.g., a fluid lumen or tube, or it may be part ofa separate instrument. Alternatively, an electrically conducting gel orspray, such as a saline electrolyte or other conductive gel, may beapplied the target site. In this embodiment, the apparatus may not havea fluid delivery element. In both embodiments, the electricallyconducting fluid will preferably generate a current flow path betweenthe electrode terminal(s) and one or more return electrode(s). In anexemplary embodiment, the return electrode is located on the probe andspaced a sufficient distance from the electrode terminal(s) tosubstantially avoid or minimize current shorting therebetween and toshield the return electrode from tissue at the target site.

In a specific configuration, the electrosurgical probe will include anelectrically insulating electrode support member having a tissuetreatment surface at the distal end of the probe. One or more electrodeterminal(s) are coupled to, or integral with, the electrode supportmember such that the electrode terminal(s) are spaced from the returnelectrode. In one embodiment, the probe includes an electrode arrayhaving a plurality of electrically isolated electrode terminals embeddedinto the electrode support member such that the electrode terminalsextend about 0.2 mm to about 10 mm distally from the tissue treatmentsurface of the electrode support member. In this embodiment, the probewill further include one or more lumens for delivering electricallyconductive fluid to one or more openings around the tissue treatmentsurface of the electrode support member. In an exemplary embodiment, thelumen will extend through a fluid tube exterior to the probe shaft thatends proximal to the return electrode.

The system may optionally include a temperature controller coupled toone or more temperature sensors at or near the distal end of the probe.The controller adjusts the output voltage of the power supply inresponse to a temperature set point and the measured temperature value.The temperature sensor may be, for example, a thermocouple, located inthe insulating support that measures a temperature at the distal end ofthe probe. In this embodiment, the temperature set point will preferablybe one that corresponds to a tissue temperature that results, forexample, in the contraction of the collagen tissue, i.e., about 60° C.to 70° C. Alternatively, the temperature sensor may directly measure thetissue temperature (e.g., infrared sensor).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis according tothe present invention;

FIG. 2 is a side view of an electrosurgical probe according to thepresent invention;

FIG. 3 is a cross-sectional view of a distal portion of the probe ofFIG. 2; FIG. 4 is an end view of the probe of FIG. 2, illustrating anarray of active electrode terminals;

FIG. 5 is an exploded view of the electrical connections within theprobe of FIG. 2;

FIGS. 6-10 are end views of alternative embodiments of the probe of FIG.2, incorporating aspiration electrode(s);

FIGS. 11A-11C. illustrate an alternative embodiment incorporating a meshelectrode for ablating aspirated tissue fragments;

FIGS. 12-15 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention;

FIG. 16 is a schematic view of the proximal portion of anotherelectrosurgical system for endoscopic spine surgery incorporating anelectrosurgical instrument according to the present invention;

FIG. 17 is an enlarged view of a distal portion of the electrosurgicalinstrument of FIG. 16;

FIG. 18 illustrates a method of ablating a volume of tissue from thenucleus pulposis of a herniated disc with the electrosurgical system ofFIG. 16;

FIG. 19 illustrates a planar ablation probe for ablating tissue inconfined spaces within a patient's body according to the presentinvention;

FIG. 20 illustrates a distal portion of the planar ablation probe ofFIG. 19;

FIG. 21A is a front sectional view of the planar ablation probe,illustrating an array of semi-cylindrical active electrodes;

FIG. 21B is a front sectional view of an alternative planar ablationprobe, illustrating an array of active electrodes having oppositepolarities;

FIG. 22 is a top, partial section, view of the working end of the planarablation probe of FIG. 19;

FIG. 23 is a side cross-sectional view of the working end of the planarablation probe, illustrating the electrical connection with one of theactive electrodes of FIG. 22;

FIG. 24 is a side cross-sectional view of the proximal end of the planarablation probe, illustrating the electrical connection with a powersource connector;

FIG. 25 is a schematic view illustrating the ablation of meniscus tissuelocated close to particular cartilage between the tibia and femur of apatient with the ablation probe of FIG. 19;

FIG. 26 is an enlarged view of the distal portion of the planar ablationprobe, illustrating ablation or cutting of meniscus tissue;

FIG. 27 illustrates a method of ablating tissue with a planar ablationprobe incorporating a single active electrode;

FIG. 28 is a schematic view illustrating the ablation of soft tissuefrom adjacent surfaces of the vertebrae with the planar ablation probeof the present invention;

FIG. 29 is a perspective view of an alternative embodiment of the planarablation probe incorporating a ceramic support structure with conductivestrips printed thereon;

FIG. 30 is a top partial cross-sectional view of the planar ablationprobe of FIG. 29;

FIG. 31 is an end view of the probe of FIG. 30;

FIGS. 32A and 32B illustrate an alternative cage aspiration electrodefor use with the electrosurgical probes shown in FIGS. 2-11;

FIGS. 33A-33C illustrate an alternative dome shaped aspiration electrodefor use with the electrosurgical probes of FIGS. 2-11; and

FIGS. 34-36 illustrates another system and method of the presentinvention for percutaneously contracting collagen fibers within a spinaldisc with a small, needle-sized instrument.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including tissue or other body structures in thespine. These procedures include laminectomy/disketomy procedures fortreating herniated disks, decompressive laminectomy for stenosis in thelumbosacral and cervical spine, medial facetectomy, posteriorlumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andanterior cervical and lumbar diskectomies. These procedures may beperformed through open procedures, or using minimally invasivetechniques, such as thoracoscopy, arthroscopy, laparascopy or the like.

In the present invention, high frequency (RF) electrical energy isapplied to one or more electrode terminals in the presence ofelectrically conductive fluid to remove and/or modify the structure oftissue structures. Depending on the specific procedure, the presentinvention may be used to: (1) volumetrically remove tissue, bone,ligament or cartilage (i.e., ablate or effect molecular dissociation ofthe body structure); (2) cut or resect tissue or other body structures;(3) shrink or contract collagen connective tissue; and/or (4) coagulatesevered blood vessels.

In some procedures, e.g., shrinkage of nucleus pulposis in herniateddiscs, it is desired to shrink or contract collagen connective tissue atthe target site. In these procedures, the RF energy heats the tissuedirectly by virtue of the electrical current flow therethrough, and/orindirectly through the exposure of the tissue to fluid heated by RFenergy, to elevate the tissue temperature from normal body temperatures(e.g., 37° C.) to temperatures in the range of 45° C. to 90° C.,preferably in the range from about 60° C. to 70° C. Thermal shrinkage ofcollagen fibers occurs within a small temperature range which, formammalian collagen is in the range from 60° C. to 70° C. (Deak, G., etal., “The Thermal Shrinkage Process of Collagen Fibres as Revealed byPolarization Optical Analysis of Topooptical Staining Reactions,” ActaMorphologica Acad. Sci. of Hungary, Vol. 15(2), pp 195-208, 1967).Collagen fibers typically undergo thermal shrinkage in the range of 60°C. to about 70° C. Previously reported research has attributed thermalshrinkage of collagen to the cleaving of the internal stabilizingcross-linkages within the collagen matrix (Deak, ibid). It has also beenreported that when the collagen temperature is increased above 70° C.,the collagen matrix begins to relax again and the shrinkage effect isreversed resulting in no net shrinkage (Allain, J. C., et al.,“Isometric Tensions Developed During the Hydrothermal Swelling of RatSkin,” Connective Tissue Research, Vol. 7, pp 127-133, 1980).Consequently, the controlled heating of tissue to a precise depth iscritical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580, filed Oct. 2, 1997, entitled “SYSTEMSAND METHODS FOR ELECTROSURGICAL TISSUE CONTRACTION”, previouslyincorporated herein by reference.

The preferred depth of heating to effect the shrinkage of collagen inthe heated region (i.e., the depth to which the tissue is elevated totemperatures between 60° C. to 70° C.) generally depends on (1) thethickness of the tissue, (2) the location of nearby structures (e.g.,nerves) that should not be exposed to damaging temperatures, and/or (3)the volume of contraction desired to relieve pressure on the spinalnerve. The depth of heating is usually in the range from 0 to 3.5 mm. Inthe case of collagen within the nucleus pulposis, the depth of heatingis preferably in the range from about 0 to about 2.0 mm.

In another method of the present invention, the tissue structures arevolumetrically removed or ablated. In this procedure, a high frequencyvoltage difference is applied between one or more electrode terminal(s)and one or more return electrode(s) to develop high electric fieldintensities in the vicinity of the target tissue site. The high electricfield intensities lead to electric field induced molecular breakdown oftarget tissue through molecular dissociation (rather than thermalevaporation or carbonization). Applicant believes that the tissuestructure is volumetrically removed through molecular disintegration oflarger organic molecules into smaller molecules and/or atoms, such ashydrogen, oxides of carbon, hydrocarbons and nitrogen compounds. Thismolecular disintegration completely removes the tissue structure, asopposed to dehydrating the tissue material by the removal of liquidwithin the cells of the tissue, as is typically the case withelectrosurgical desiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the electrode terminal(s) inthe region between the distal tip of the electrode terminal(s) and thetarget tissue. The electrically conductive fluid may be a gas or liquid,such as isotonic saline, delivered to the target site, or a viscousfluid, such as a gel, that is located at the target site. In the latterembodiment, the electrode terminal(s) are submersed in the electricallyconductive gel during the surgical procedure. Since the vapor layer orvaporized region has a relatively high electrical impedance, itincreases the voltage differential between the electrode terminal tipand the tissue and causes ionization within the vapor layer due to thepresence of an ionizable species (e.g., sodium when isotonic saline isthe electrically conducting fluid). This ionization, under optimalconditions, induces the discharge of energetic electrons and photonsfrom the vapor layer and to the surface of the target tissue. Thisenergy may be in the form of energetic photons (e.g., ultravioletradiation), energetic particles (e.g., electrons) or a combinationthereof. A more detailed description of this cold ablation phenomena,termed Coblation™, can be found in commonly assigned U.S. Pat. No.5,683,366 the complete disclosure of which is incorporated herein byreference.

The present invention applies high frequency (RF) rical energy in anelectrically conducting fluid environment to remove (i.e., resect, cutor ablate) or contract a tissue structure, and to seal transectedvessels within the region of the target tissue. The present invention isparticularly useful for sealing larger arterial vessels, e.g., on theorder of 1 mm or greater. In some embodiments, a high frequency powersupply is provided having an ablation mode, wherein a first voltage isapplied to an electrode terminal sufficient to effect moleculardissociation or disintegration of the tissue, and a coagulation mode,wherein a second, lower voltage is applied to an electrode terminal(either the same or a different electrode) sufficient to achievehemostasis of severed vessels within the tissue. In other embodiments,an electrosurgical probe is provided having one or more coagulationelectrode(s) configured for sealing a severed vessel, such as anarterial vessel, and one or more electrode terminals configured foreither contracting the collagen fibers within the tissue or removing(ablating) the tissue, e.g., by applying sufficient energy to the tissueto effect molecular dissociation. In the latter embodiments, thecoagulation electrode(s) may be configured such that a single voltagecan be applied to coagulate with the coagulation electrode(s), and toablate or contract with the electrode terminal(s). In other embodiments,the power supply is combined with the coagulation probe such that thecoagulation electrode is used when the power supply is in thecoagulation mode (low voltage), and the electrode terminal(s) are usedwhen the power supply is in the ablation mode (higher voltage).

In the method of the present invention, one or more electrode terminalsare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the electrode terminals and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the electrode terminals may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent probe may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

The present invention is particularly useful for removing or ablatingtissue around nerves, such as spinal or cranial nerves, e.g., the spinalcord and the surrounding dura mater. One of the significant drawbackswith the prior art cutters, graspers, and lasers is that these devicesdo not differentiate between the target tissue and the surroundingnerves or bone. Therefore, the surgeon must be extremely careful duringthese procedures to avoid damage to the bone or nerves within and aroundthe spinal cord. In the present invention, the Coblation™ process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Nerves usually comprise a connective tissue sheath, or endoneurium,enclosing the bundles of nerve fibers to protect these nerve fibers.This protective tissue sheath typically comprises a fatty tissue (e.g.,adipose tissue) having substantially different electrical propertiesthan the normal target tissue, such as the disc and other surroundingtissue that are, for example, removed from the spine during spinalprocedures. The system of the present invention measures the electricalproperties of the tissue at the tip of the probe with one or moreelectrode terminal(s). These electrical properties may includeelectrical conductivity at one, several or a range of frequencies (e.g.,in the range from 1 kHz to 100 MHz), dielectric constant, capacitance orcombinations of these. In this embodiment, an audible signal may beproduced when the sensing electrode(s) at the tip of the probe detectsthe fatty tissue surrounding a nerve, or direct feedback control can beprovided to only supply power to the electrode terminal(s) eitherindividually or to the complete array of electrodes, if and when thetissue encountered at the tip or working end of the probe is normaltissue based on the measured electrical properties.

In one embodiment, the current limiting elements (discussed in detailabove) are configured such that the electrode terminals will shut downor turn off when the electrical impedance reaches a threshold level.When this threshold level is set to the impedance of the fatty tissuesurrounding nerves, the electrode terminals will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother electrode terminals, which are in contact with or in closeproximity to nasal tissue, will continue to conduct electric current tothe return electrode. This selective ablation or removal of lowerimpedance tissue in combination with the Coblation™ mechanism of thepresent invention allows the surgeon to precisely remove tissue aroundnerves or bone.

In addition to the above, applicant has discovered that the Coblation™mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the electrode terminal(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of electrode terminals;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 to 5 eV to break.Accordingly, the present invention in its current configurationgenerally does not ablate or remove such fatty tissue. Of course,factors may be changed such that these double bonds can be broken (e.g.,increasing voltage or changing the electrode configuration to increasethe current density at the electrode tips).

The electrosurgical probe or catheter will comprise a shaft or ahandpiece having a proximal end and a distal end which supports one ormore electrode terminal(s). The shaft or handpiece may assume a widevariety of configurations, with the primary purpose being tomechanically support the active electrode and permit the treatingphysician to manipulate the electrode from a proximal end of the shaft.The shaft may be rigid or flexible, with flexible shafts optionallybeing combined with a generally rigid external tube for mechanicalsupport. Flexible shafts may be combined with pull wires, shape memoryactuators, and other known mechanisms for affecting selective deflectionof the distal end of the shaft to facilitate positioning of theelectrode array. The shaft will usually include a plurality of wires orother conductive elements running axially therethrough to permitconnection of the electrode array to a connector at the proximal end ofthe shaft.

For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc) by delivering the shaft through the thoracic cavity,the abdomen or the like. Thus, the shaft will usually have a length inthe range of about 5.0 to 30.0 cm, and a diameter in the range of about0.2 mm to about 20 mm. Alternatively, the shaft may be delivereddirectly through the patient's back in a posterior approach, which wouldconsiderably reduce the required length of the shaft. In any of theseembodiments, the shaft may also be introduced through rigid or flexibleendoscopes. Specific shaft designs will be described in detail inconnection with the figures hereinafter.

In an alternative embodiment, the probe may comprise a long, thin needle(e.g., on the order of about 1 mm in diameter or less) that can bepercutaneously introduced through the patient's back directly into thespine (see FIGS. 34-36). The needle will include one or more activeelectrode(s) for applying electrical energy to tissues within the spine.The needle may include one or more return electrode(s), or the returnelectrode may be positioned on the patient's back, as a dispersive pad.In either embodiment, sufficient electrical energy is applied throughthe needle to the active electrode(s) to either shrink the collagenfibers within the spinal disk, or to ablate tissue within the disk.

The current flow path between the electrode terminal(s) and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a liquid or a viscous fluid,such as an electrically conductive gel) or by directing an electricallyconducting fluid along a fluid path to the target site (i.e., a liquid,such as isotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conducting fluid provides asuitable current flow path from the electrode terminal to the returnelectrode. A more complete description of an exemplary method ofdirecting electrically conducting fluid between the active and returnelectrodes is described in U.S. Pat. No. 5,697,536, previouslyincorporated herein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid after it has been directed to the targetsite. In addition, it may be desirable to aspirate small pieces oftissue that are not completely disintegrated by the high frequencyenergy, or other fluids at the target site, such as blood, mucus, thegaseous products of ablation, etc. Accordingly, the system of thepresent invention will usually include a suction lumen in the probe, oron another instrument, for aspirating fluids from the target site. Inaddition, the invention may include one or more aspiration electrode(s)coupled to the distal end of the suction lumen for ablating, or at leastreducing the volume of, non-ablated tissue fragments that are aspiratedinto the lumen. The aspiration electrode(s) function mainly to inhibitclogging of the lumen that may otherwise occur as larger tissuefragments are drawn therein. The aspiration electrode(s) may bedifferent from the ablation electrode terminal(s), or the sameelectrode(s) may serve both functions. A more complete description ofprobes incorporating aspiration electrode(s) can be found in commonlyassigned, co-pending patent application entitled “SYSTEMS AND METHODSFOR TISSUE RESECTION, ABLATION AND ASPIRATION”, filed Jan. 21, 1998, thecomplete disclosure of which is incorporated herein by reference.

The present invention may use a single active electrode terminal or anelectrode array distributed over a contact surface of a probe. In thelatter embodiment, the electrode array usually includes a plurality ofindependently current-limited and/or power-controlled electrodeterminals to apply electrical energy selectively to the target tissuewhile limiting the unwanted application of electrical energy to thesurrounding tissue and environment resulting from power dissipation intosurrounding electrically conductive liquids, such as blood, normalsaline, electrically conductive gel and the like. The electrodeterminals may be independently current-limited by isolating theterminals from each other and connecting each terminal to a separatepower source that is isolated from the other electrode terminals.Alternatively, the electrode terminals may be connected to each other ateither the proximal or distal ends of the probe to form a single wirethat couples to a power source.

In some embodiments, the active electrode(s) have an active portion orsurface with surface geometries shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and target tissue to facilitate ablationor cutting of the tissue. For example, surface asperities may be createdby etching the active electrodes with etchants having a Ph less than 7.0or by using a high velocity stream of abrasive particles (e.g., gritblasting) to create asperities on the surface of an elongated electrode.

The active electrode(s) are typically mounted in an electricallyinsulating electrode support that extends from the electrosurgicalprobe. In some embodiments, the electrode support comprises a pluralityof wafer layers bonded together, e.g., by a glass adhesive or the like,or a single wafer. The wafer layer(s) have conductive strips printedthereon to form the electrode terminal(s) and the return electrode(s).In one embodiment, the proximal end of the wafer layer(s) will have anumber of holes extending from the conductor strips to an exposedsurface of the wafer layers for connection to electrical conductor leadtraces in the electrosurgical probe or handpiece. The wafer layerspreferably comprise a ceramic material, such as alumina, and theelectrode will preferably comprise a metallic material, such as gold,copper, platinum, palladium, tungsten, silver or the like. Suitablemultilayer ceramic electrodes are commercially available from e.g.,VisPro Corporation of Beaverton, Oreg.

In one configuration, each individual electrode terminal in theelectrode array is electrically insulated from all other electrodeterminals in the array within said probe and is connected to a powersource which is isolated from each of the other electrode terminals inthe array or to circuitry which limits or interrupts current flow to theelectrode terminal when low resistivity material (e.g., blood,electrically conductive saline irrigant or electrically conductive gel)causes a lower impedance path between the return electrode and theindividual electrode terminal. The isolated power sources for eachindividual electrode terminal may be separate power supply circuitshaving internal impedance characteristics which limit power to theassociated electrode terminal when a low impedance return path isencountered. By way of example, the isolated power source may be a userselectable constant current source. In this embodiment, lower impedancepaths will automatically result in lower resistive heating levels sincethe heating is proportional to the square of the operating current timesthe impedance. Alternatively, a single power source may be connected toeach of the electrode terminals through independently actuatableswitches, or by independent current limiting elements, such asinductors, capacitors, resistors and/or combinations thereof. Thecurrent limiting elements may be provided in the probe, connectors,cable, controller or along the conductive path from the controller tothe distal tip of the probe. Alternatively, the resistance and/orcapacitance may occur on the surface of the active electrode terminal(s)due to oxide layers which form the electrode terminals (e.g., titaniumor a resistive coating on the surface of metal, such as platinum).

The tip region of the probe may comprise many independent electrodeterminals designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual electrode terminal andthe return electrode to a power source having independently controlledor current limited channels. The return electrode(s) may comprise asingle tubular member of conductive material proximal to the electrodearray at the tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the probe may comprise an array of return electrodes atthe distal tip of the probe (together with the active electrodes) tomaintain the electric current at the tip. The application of highfrequency voltage between the return electrode(s) and the electrodearray results in the generation of high electric field intensities atthe distal tips of the electrode terminals with conduction of highfrequency current from each individual electrode terminal to the returnelectrode. The current flow from each individual electrode terminal tothe return electrode(s) is controlled by either active or passive means,or a combination thereof, to deliver electrical energy to thesurrounding conductive fluid while minimizing energy delivery tosurrounding (non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the electrode terminal(s) for appropriate timeintervals effects cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. The tissue volume over whichenergy is dissipated (i.e., a high current density exists) may beprecisely controlled, for example, by the use of a multiplicity of smallelectrode terminals whose effective diameters or principal dimensionsrange from about 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm,and more preferably from about 1 mm to 0.1 mm. Electrode areas for bothcircular and non-circular terminals will have a contact area (perelectrode terminal) below 25 mm², preferably being in the range from0.0001 mm² to 1 mm², and more preferably from 0.005 mm² to 0.5 mm². Thecircumscribed area of the electrode array is in the range from 0.25 mm²to 200 mm², preferably from 0.5 mm² to 100 mm², and will usually includeat least two isolated electrode terminals, preferably at least fiveelectrode terminals, often greater than 10 electrode terminals and even50 or more electrode terminals, disposed over the distal contactsurfaces on the shaft. The use of small diameter electrode terminalsincreases the electric field intensity and reduces the extent or depthof tissue heating as a consequence of the divergence of current fluxlines which emanate from the exposed surface of each electrode terminal.

The area of the tissue treatment surface can vary widley, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Activeelectrode surfaces can have areas in the range from 0.25 mm² to 75 mm²,usually being from about 0.5 mm² to 40 mm². The geometries can beplanar, concave, convex, hemispherical, conical, linear “in-line” arrayor virtually any other regular or irregular shape. Most commonly, theactive electrode(s) or electrode terminal(s) will be formed at thedistal tip of the electrosurgical probe shaft, frequently being planar,disk-shaped, or hemispherical surfaces for use in reshaping proceduresor being linear arrays for use in cutting. Alternatively oradditionally, the active electrode(s) may be formed on lateral surfacesof the electrosurgical probe shaft (e.g., in the manner of a spatula),facilitating access to certain body structures in endoscopic procedures.

The electrically conducting fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode(s)and the electrode terminal(s). The electrical conductivity of the fluid(in units of milliSiemans per centimeter or mS/cm) will usually begreater than 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Alternatively, the fluid may be anelectrically conductive gel or spray, such as a saline electrolyte gel,a conductive ECG spray, an electrode conductivity gel, an ultrasoundtransmission or scanning gel, or the like. Suitable gels or sprays arecommercially available from Graham-Field, Inc of Hauppauge, N.Y.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the probe or handpiece to confine theelectrically conductive fluid to the region immediately surrounding theelectrode support. In addition, the shaft may be shaped so as to form acavity around the electrode support and the fluid outlet. This helps toassure that the electrically conductive fluid will remain in contactwith the electrode terminal(s) and the return electrode(s) to maintainthe conductive path therebetween. In addition, this will help tomaintain a vapor or plasma layer between the electrode terminal(s) andthe tissue at the treatment site throughout the procedure, which reducesthe thermal damage that might otherwise occur if the vapor layer wereextinguished due to a lack of conductive fluid. Provision of theelectrically conductive fluid around the target site also helps tomaintain the tissue temperature at desired levels.

The voltage applied between the return electrode(s) and the electrodearray will be at high or radio frequency, typically between about 5 kHzand 20 MHz, usually being between about 30 kHz and 2.5 MHz, preferablybeing between about 50 kHz and 500 kHz, more preferably less than 350kHz, and most preferably between about 100 kHz and 200 kHz. The RMS(root mean square) voltage applied will usually be in the range fromabout 5 volts to 1000 volts, preferably being in the range from about 10volts to 500 volts depending on the electrode terminal size, theoperating frequency and the operation mode of the particular procedureor desired effect on the tissue (i.e., contraction, coagulation orablation). Typically, the peak-to-peak voltage will be in the range of10 to 2000 volts, preferably in the range of 20 to 1200 volts and morepreferably in the range of about 40 to 800 volts (again, depending onthe electrode size, the operating frequency and the operation mode).

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e.,cumulative time in any one-second interval that energy is applied) is onthe order of about 50% for the present invention, as compared withpulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip. The power source allows the userto select the voltage level according to the specific requirements of aparticular spine procedure, arthroscopic surgery, dermatologicalprocedure, ophthalmic procedures, FESS procedure, open surgery or otherendoscopic surgery procedure. A description of a suitable power sourcecan be found in U.S. Provisional Patent Application No. 60/1062,997entitled “SYSTEMS AND METHODS FOR ELECTROSURGICAL TISSUE AND FLUIDCOAGULATION”, filed Oct. 23, 1997, the complete disclosure of which hasbeen incorporated herein by reference.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent electrode terminal, where the inductance of theinductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously inco-pending PCT application No. PCT/US94/05168, the complete disclosureof which is incorporated herein by reference. Additionally, currentlimiting resistors may be selected. Preferably, these resistors have alarge positive temperature coefficient of resistance so that, as thecurrent level begins to rise for any individual electrode terminal incontact with a low resistance medium (e.g., saline irrigant orconductive gel), the resistance of the current limiting resistorincreases significantly, thereby minimizing the power delivery from saidelectrode terminal into the low resistance medium (e.g., saline irrigantor conductive gel).

It should be clearly understood that the invention is not limited toelectrically isolated electrode terminals, or even to a plurality ofelectrode terminals. For example, the array of active electrodeterminals may be connected to a single lead that extends through theprobe shaft to a power source of high frequency current. Alternatively,the probe may incorporate a single electrode that extends directlythrough the probe shaft or is connected to a single lead that extends tothe power source. The active electrode may have a ball shape (e.g., fortissue vaporization and desiccation), a twizzle shape (for vaporizationand needle-like cutting), a spring shape (for rapid tissue debulking anddesiccation), a twisted metal shape, an annular or solid tube shape orthe like. Alternatively, the electrode may comprise a plurality offilaments, a rigid or flexible brush electrode (for debulking a tumor,such as a fibroid, bladder tumor or a prostate adenoma), a side-effectbrush electrode on a lateral surface of the shaft, a coiled electrode orthe like. In one embodiment, the probe comprises a single activeelectrode terminal that extends from an insulating member, e.g.,ceramic, at the distal end of the probe. The insulating member ispreferably a tubular structure that separates the active electrodeterminal from a tubular or annular return electrode positioned proximalto the insulating member and the active electrode.

Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site and a fluid source 21 for supplyingelectrically conducting fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, particularly inendoscopic spine procedures. The endoscope may be integral with probe10, or it may be part of a separate instrument. The system 11 may alsoinclude a vacuum source (not shown) for coupling to a suction lumen ortube 211 (see FIG. 2) in the probe 10 for aspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of electrode terminals 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the electrode terminals 58 to power supply 28. The electrodeterminals 58 are electrically isolated from each other and each of theterminals is connected to an active or passive control network withinpower supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conducting fluid 50 tothe target site.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to electrode terminals 58. Inan exemplary embodiment, first foot pedal 37 is used to place the powersupply into the “ablation” mode and second foot pedal 38 places powersupply 28 into the “coagulation” mode. The third foot pedal 39 allowsthe user to adjust the voltage level within the “ablation” mode. In theablation mode, a sufficient voltage is applied to the electrodeterminals to establish the requisite conditions for moleculardissociation of the tissue (i.e., vaporizing a portion of theelectrically conductive fluid, ionizing charged particles within thevapor layer and accelerating these charged particles against thetissue). As discussed above, the requisite voltage level for ablationwill vary depending on the number, size, shape and spacing of theelectrodes, the distance in which the electrodes extend from the supportmember, etc.

Once the surgeon places the power supply in the “ablation” mode, voltagelevel adjustment or third foot pedal 39 may be used to adjust thevoltage level to adjust the degree or aggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the coagulation mode, the power supply 28 applies a low enoughvoltage to the electrode terminals (or the coagulation electrode) toavoid vaporization of the electrically conductive fluid and subsequentmolecular dissociation of the tissue. The surgeon may automaticallytoggle the power supply between the ablation and coagulation modes byalternatively stepping on foot pedals 37, 38, respectively. This allowsthe surgeon to quickly move between coagulation and ablation in situ,without having to remove his/her concentration from the surgical fieldor without having to request an assistant to switch the power supply. Byway of example, as the surgeon is sculpting soft tissue in the ablationmode, the probe typically will simultaneously seal and/or coagulationsmall severed vessels within the tissue. However, larger vessels, orvessels with high fluid pressures (e.g., arterial vessels) may not besealed in the ablation mode. Accordingly, the surgeon can simply step onfoot pedal 38, automatically lowering the voltage level below thethreshold level for ablation, and apply sufficient pressure onto thesevered vessel for a sufficient period of time to seal and/or coagulatethe vessel. After this is completed, the surgeon may quickly move backinto the ablation mode by stepping on foot pedal 37. A specific designof a suitable power supply for use with the present invention can befound in U.S. Provisional Patent Application No. 60/062,997, entitled“SYSTEMS AND METHODS FOR ELECTROSURGICAL TISSUE AND FLUID COAGULATION”,filed Oct. 23, 1997, previously incorporated herein by reference.

FIGS. 2-5 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.2, probe 20 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises a plastic material that is easilymolded into the shape shown in FIG. 2. In an alternative embodiment (notshown), shaft 100 comprises an electrically conducting material, usuallymetal, which is selected from the group comprising tungsten, stainlesssteel alloys, platinum or its alloys, titanium or its alloys, molybdenumor its alloys, and nickel or its alloys. In this embodiment, shaft 100includes an electrically insulating jacket 108, which is typicallyformed as one or more electrically insulating sheaths or coatings, suchas polytetrafluoroethylene, polyimide, and the like. The provision ofthe electrically insulating jacket over the shaft prevents directelectrical contact between these metal elements and any adjacent bodystructure or the surgeon. Such direct electrical contact between a bodystructure (e.g., tendon) and an exposed electrode could result inunwanted heating and necrosis of the structure at the point of contactcausing necrosis.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 5), and provides a suitable interface for connection to anelectrical connecting cable 22 (see FIG. 1). Electrode support member102 extends from the distal end of shaft 100 (usually about 1 to 20 mm),and provides support for a plurality of electrically isolated electrodeterminals 104 (see FIG. 4). As shown in FIG. 2, a fluid tube 233 extendsthrough an opening in handle 204, and includes a connector 235 forconnection to a fluid supply source, for supplying electricallyconductive fluid to the target site. Fluid tube 233 is coupled to adistal fluid tube 239 that extends along the outer surface of shaft 100to an opening 237 at the distal end of the probe 20, as discussed indetail below. Of course, the invention is not limited to thisconfiguration. For example, fluid tube 233 may extend through a singlelumen (not shown) in shaft 100, or it may be coupled to a plurality oflumens (also not shown) that extend through shaft 100 to a plurality ofopenings at its distal end. Probe 20 may also include a valve 17(FIG. 1) or equivalent structure for controlling the flow rate of theelectrically conducting fluid to the target site.

As shown in FIGS. 3 and 4, electrode support member 102 has asubstantially planar tissue treatment surface 212 and comprises asuitable insulating material (e.g., ceramic or glass material, such asalumina, zirconia and the like) which could be formed at the time ofmanufacture in a flat, hemispherical or other shape according to therequirements of a particular procedure. The preferred support membermaterial is alumina, available from Kyocera Industrial CeramicsCorporation, Elkgrove, Ill., because of its high thermal conductivity,good electrically insulative properties, high flexural modulus,resistance to carbon tracking, biocompatibility, and high melting point.The support member 102 is adhesively joined to a tubular support member(not shown) that extends most or all of the distance between supportmember 102 and the proximal end of probe 20. The tubular memberpreferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

In a preferred construction technique, electrode terminals 104 extendthrough pre-formed openings in the support member 102 so that theyprotrude above tissue treatment surface 212 by the desired distance. Theelectrodes are then bonded to the tissue treatment surface 212 ofsupport member 102, typically by an inorganic sealing material. Thesealing material is selected to provide effective electrical insulation,and good adhesion to both the alumina member 102 and the platinum ortitanium electrode terminals 104. The sealing material additionallyshould have a compatible thermal expansion coefficient and a meltingpoint well below that of platinum or titanium and alumina or zirconia,typically being a glass or glass ceramic

In the embodiment shown in FIGS. 2-5, probe 20 includes a returnelectrode 112 for completing the current path between electrodeterminals 104 and a high frequency power supply 28 (see FIG. 1). Asshown, return electrode 112 preferably comprises an annular conductiveband coupled to the distal end of shaft 100 slightly proximal to tissuetreatment surface 212 of electrode support member 102, typically about0.5 to 10 mm and more preferably about 1 to 10 mm. Return electrode 112is coupled to a connector 258 that extends to the proximal end of probe10, where it is suitably connected to power supply 10 (FIG. 1).

As shown in FIG. 2, return electrode 112 is not directly connected toelectrode terminals 104. To complete this current path so that electrodeterminals 104 are electrically connected to return electrode 112,electrically conducting fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconducting fluid is delivered through an external fluid tube 239 toopening 237, as described above. Alternatively, the fluid may bedelivered by a fluid delivery element (not shown) that is separate fromprobe 20. In some microendoscopic discectomy procedures, for example,the trocar cannula may be flooded with isotonic saline and the probe 20will be introduced into this flooded cavity. Electrically conductingfluid will be continually resupplied with a separate instrument tomaintain the conduction path between return electrode 112 and electrodeterminals 104.

In alternative embodiments, the fluid path may be formed in probe 20 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (not shown).This annular gap may be formed near the perimeter of the shaft 100 suchthat the electrically conducting fluid tends to flow radially inwardtowards the target site, or it may be formed towards the center of shaft100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in parentapplication U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995, the completedisclosure of which has previously been incorporated herein byreference.

Referring to FIG. 4, the electrically isolated electrode terminals 104are spaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual electrodeterminals 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range ofabout 1 mm to 30 mm, usually about 2 to 20 mm. The individual electrodeterminals 104 preferably extend outward from tissue treatment surface212 by a distance of about 0.1 to 8 mm, usually about 0.2 to 4 mm.Applicant has found that this configuration increases the high electricfield intensities and associated current densities around electrodeterminals 104 to facilitate the ablation of tissue as described indetail above.

In the embodiment of FIGS. 2-5, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of electrode terminals (e.g., about 3-15) around the perimeterof surface 212 (see FIG. 3). Alternatively, the probe may include asingle, annular, or partially annular, electrode terminal at theperimeter of the tissue treatment surface. The central opening 209 iscoupled to a suction or aspiration lumen 213 (see FIG. 2) within shaft100 and a suction tube 211 (FIG. 2) for aspirating tissue, fluids and/orgases from the target site. In this embodiment, the electricallyconductive fluid generally flows from opening 237 of fluid tube 239radially inward past electrode terminals 104 and then back through thecentral opening 209 of support member 102. Aspirating the electricallyconductive fluid during surgery allows the surgeon to see the targetsite, and it prevents the fluid from flowing into the patient's body,e.g., into the spine, the abdomen or the thoracic cavity. Thisaspiration should be controlled, however, so that the conductive fluidmaintains a conductive path between the active electrode terminal(s) andthe return electrode.

Of course, it will be recognized that the distal tip of probe may have avariety of different configurations. For example, the probe may includea plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (this embodiment not shown in the drawings). Inthis embodiment, the electrode terminals 104 extend from the center oftissue treatment surface 212 radially inward from openings 209. Theopenings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and aspiration lumen213 for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the electrode terminals 104.

In some embodiments, the probe 20 will also include one or moreaspiration electrode(s) coupled to the aspiration lumen for inhibitingclogging during aspiration of tissue fragments from the surgical site.As shown in FIG. 6, one or more of the active electrode terminals 104may comprise loop electrodes 140 that extend across distal opening 209of the suction lumen within shaft 100. In the representative embodiment,two of the electrode terminals 104 comprise loop electrodes 140 thatcross over the distal opening 209. Of course, it will be recognized thata variety of different configurations are possible, such as a singleloop electrode, or multiple loop electrodes having differentconfigurations than shown. In addition, the electrodes may have shapesother than loops, such as the coiled configurations shown in FIGS. 6 and7. Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 8. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

Loop electrodes 140 are electrically isolated from the other electrodeterminals 104, which can be referred to hereinafter as the ablationelectrodes 104. Loop electrodes 140 may or may not be electricallyisolated from each other. Loop electrodes 140 will usually extend onlyabout 0.05 to 4 mm, preferably about 0.1 to 1 mm from the tissuetreatment surface of electrode support member 104.

Referring now to FIGS. 7 and 8, alternative embodiments for aspirationelectrodes will now be described. As shown in FIG. 7, the aspirationelectrodes may comprise a pair of coiled electrodes 150 that extendacross distal opening 209 of the suction lumen. The larger surface areaof the coiled electrodes 150 usually increases the effectiveness of theelectrodes 150 on tissue fragments passing through opening 209. In FIG.8, the aspiration electrode comprises a single coiled electrode 152passing across the distal opening 209 of suctioumen. This singleelectrode 152 may be sufficient to inhibit clogging of the suctionlumen. Alternatively, the aspiration electrodes may be positioned withinthe suction lumen proximal to the distal opening 209. Preferably, theseelectrodes are close to opening 209 so that tissue does not clog theopening 209 before it reaches electrodes 154. In this embodiment, aseparate return electrode 156 may be provided within the suction lumento confine the electric currents therein.

Referring to FIG. 10, another embodiment of the present inventionincorporates an aspiration electrode 160 within the aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representation embodiment, the aspirationelectrode 160 comprises a loop electrode that stretches across theaspiration lumen 162. However, it will be recognized that many otherconfigurations are possible. In this embodiment, the return electrode164 is located outside of the probe as in the previously embodiments.Alternatively, the return electrode(s) may be located within theaspiration lumen 162 with the aspiration electrode 160. For example, theinner insulating coating 163 may be exposed at portions within the lumen162 to provide a conductive path between this exposed portion of returnelectrode 164 and the aspiration electrode 160. The latter embodimenthas the advantage of confining the electric currents to within theaspiration lumen. In addition, in dry fields in which the conductivefluid is delivered to the target site, it is usually easier to maintaina conductive fluid path between the active and return electrodes in thelatter embodiment because the conductive fluid is aspirated through theaspiration lumen 162 along with the tissue fragments.

Referring to FIG. 9, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowthrough into aspiration lumen 162. The size of the openings 602 willvary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of ceramic support member102. Wire mesh electrode 600 comprises a conductive material, such astitanium, tantalum, steel, stainless steel, tungsten, copper, gold orthe like. In the representative embodiment, wire mesh electrode 600comprises a different material having a different electric potentialthan the active electrode terminal(s) 104. Preferably, mesh electrode600 comprises steel and electrode terminal(s) comprises tungsten.Applicant has found that a slight variance in the electrochemicalpotential of mesh electrode 600 and electrode terminal(s) 104 improvesthe performance of the device. Of course, it will be recognized that themesh electrode may be electrically insulated from active electrodeterminal(s) as in previous embodiments

Referring noe to FIGS. 11A-11C, an alternative embodiment incorporatinga metal screen 610 is illustrated. As shown, metal screen 610 has aplurality of peripheral openings 612 for receiving electrode terminals104, and a plurality of inner openings 614 for allowing aspiration offluid and tissue through opening 609 of the aspiration lumen. As shown,screen 610 is press fitted over electrode terminals 104 and then adheredto shaft 100 of probe 20. Similar to the mesh electrode embodiment,metal screen 610 may comprise a variety of conductive metals, such astitanium, tantalum, steel, stainless steel, tungsten, copper, gold orthe like. In the representative embodiment, metal screen 610 is coupleddirectly to, or integral with, active electrode terminal(s) 104. In thisembodiment, the active electrode terminal(s) 104 and the metal screen610 are electrically coupled to each other.

FIGS. 32 and 33 illustrate alternative embodiments of the mesh andscreen aspiration electrodes. As shown in FIG. 32A and 32B, the probemay include a conductive cage electrode 620 that extends into theaspiration lumen 162 (not shown) to increase the effect of the electrodeon aspirated tissue. FIGS. 33A-33C illustrate a dome-shaped screenelectrode 630 that includes one or more anchors 632 (four in therepresentative embodiment) for attaching the screen electrode 630 to aconductive spacer 634. Screen electrode 630 includes a plurality ofholes 631 for allowing fluid and tissue fragments to pass therethroughto aspiration lumen 162. Screen electrode 630 is sized to fit withinopening 609 of aspiration lumen 162 except for the anchors 632 whichinclude holes 633 for receiving electrode terminals 104. Spacer 634includes peripheral holes 636 for receiving electrode terminals 104 anda central hole 638 aligned with suction lumen 162. Spacer 634 mayfurther include insulated holes 640 for electrically isolating screenelectrode 630 from electrode terminals 104. As shown in FIG. 33C,dome-shaped screen electrode 630 preferably extends distally from theprobe shaft 100 about the same distance as the electrode terminals 104.Applicant has found that this configuration enhances the ablation ratefor tissue adjacent to electrode terminals 104, while still maintainingthe ability to ablate aspirated tissue fragments passing through screen630.

FIG. 5 illustrates the electrical connections 250 within handle 204 forcoupling electrode terminals 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple terminals 104 to a plurality of pins 254, which are pluggedinto a connector block 256 for coupling to a connecting cable 22 (FIG.1). Similarly, return electrode 112 is coupled to connector block 256via a wire 258 and a plug 260.

In some embodiments of the present invention, the probe 20 furtherincludes an identification element that is characteristic of theparticular electrode assembly so that the same power supply 28 can beused for different electrosurgical operations. In one embodiment, forexample, the probe 20 includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the electrodeterminals 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the electrode terminals and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.The voltage reduction element primarily allows the electrosurgical probe20 to be compatible with other ArthroCare generators that are adapted toapply higher voltages for ablation or vaporization of tissue. Forcontraction of tissue, for example, the voltage reduction element willserve to reduce a voltage of about 100 to 135 volts rms (which is asetting of 1 on the ArthroCare Model 970 and 980 (i.e., 2000)Generators) to about 45 to 60 volts rms, which is a suitable voltage forcontraction of tissue without ablation (e.g., molecular dissociation) ofthe tissue.

Of course, for some procedures in endoscopic spine surgery, the probewill typically not require a voltage reduction element. Alternatively,the probe may include a voltage increasing element or circuit, ifdesired.

In the representative embodiment, the voltage reduction element is adropping capacitor 262 which has first leg 264 coupled to the returnelectrode wire 258 and a second leg 266 coupled to connector block 256.Of course, the capacitor may be located in other places within thesystem, such as in, or distributed along the length of, the cable, thegenerator, the connector, etc. In addition, it will be recognized thatother voltage reduction elements, such as diodes, transistors,inductors, resistors, capacitors or combinations thereof, may be used inconjunction with the present invention. For example, the probe 90 mayinclude a coded resistor (not shown) that is constructed to lower thevoltage applied between return electrode 112 and electrode terminals 104to a suitable level for contraction of tissue. In addition, electricalcircuits may be employed for this purpose.

Alternatively or additionally, the cable 22 that couples the powersupply 10 to the probe 90 may be used as a voltage reduction element.The cable has an inherent capacitance that can be used to reduce thepower supply voltage if the cable is placed into the electrical circuitbetween the power supply, the electrode terminals and the returnelectrode. In this embodiment, the cable 22 may be used alone, or incombination with one of the voltage reduction elements discussed above,e.g., a capacitor.

In some embodiments, the probe 20 will further include a switch (notshown) or other input that allows the surgeon to couple and decouple theidentification element to the rest of the electronics in the probe 20.For example, if the surgeon would like to use the same probe forablation of tissue and contraction of tissue in the same procedure, thiscan be accomplished by manipulating the switch. Thus, for ablation oftissue, the surgeon will decouple the voltage reduction element from theelectronics so that the full voltage applied by the power source isapplied to the electrodes on the probe. When the surgeon desires toreduce the voltage to a suitable level for contraction of tissue, he/shecouples the voltage reduction element to the electronics to reduce thevoltage applied by the power supply to the electrode terminals.

Further, it should be noted that the present invention can be used witha power supply that is adapted to apply a voltage within the selectedrange for treatment of tissue. In this embodiment, a voltage reductionelement or circuitry may not be desired.

The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 12-15, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from the incision 220 to thelarnina 274. The first dilator may be used to “palpate” the lamina 274,assuring proper location of its tip between the spinous process andfacet complex just above the inferior edge of the lamina 274. As shownin FIG. 13, a tubular retractor 278 is then passed over the largestdilator down to the lamina 274. The dilators 276 are removed,establishing an operating corridor within the tubular retractor 278.

As shown in FIG. 13, an endoscope 280 is then inserted into the tubularretractor 278 and a ring clamp 282 is used to secure the endoscope 280.Typically, the formation of the operating corridor within retractor 278requires the removal of soft tissue, muscle or other types of tissuethat were forced into this corridor as the dilators 276 and retractor278 were advanced down to the lamina 274. This tissue is usually removedwith mechanical instruments, such as pituitary rongeurs, curettes,graspers, cutters, drills, microdebriders and the like. Unfortunately,these mechanical instruments greatly lengthen and increase thecomplexity of the procedure. In addition, these instruments sever bloodvessels within this tissue, usually causing profuse bleeding thatobstructs the surgeon's view of the target site.

According to the present invention, an electrosurgical probe or catheter284 as described above is introduced into the operating corridor withinthe retractor 278 to remove the soft tissue, muscle and otherobstructions from this corridor so that the surgeon can easily accessand visualization the lamina 274. Once the surgeon has reached hasintroduced the probe 284, electrically conductive fluid 285 is deliveredthrough tube 233 and opening 237 to the tissue (see FIG. 2). The fluidflows past the return electrode 112 to the electrode terminals 104 atthe distal end of the shaft. The rate of fluid flow is controlled withvalve 17 (FIG. 1) such that the zone between the tissue and electrodesupport 102 is constantly immersed in the fluid. The power supply 28 isthen turned on and adjusted such that a high frequency voltagedifference is applied between electrode terminals 104 and returnelectrode 112. The electrically conductive fluid provides the conductionpath (see current flux lines) between electrode terminals 104 and thereturn electrode 112.

The high frequency voltage is sufficient to convert the electricallyconductive fluid (not shown) between the target tissue and electrodeterminal(s)104 into an ionized vapor layer or plasma (not shown). As aresult of the applied voltage difference between electrode terminal(s)104 and the target tissue (i.e., the voltage gradient across the plasmalayer), charged particles in the plasma (viz., electrons) areaccelerated towards the tissue. At sufficiently high voltagedifferences, these charged particles gain sufficient energy to causedissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the underlying tissue.

During the process, the gases will be aspirated through opening 209 andsuction tube 211 to a vacuum source. In addition, excess electricallyconductive fluid, and other fluids (e.g., blood) will be aspirated fromthe operating corridor to facilitate the surgeon's view. During ablationof the tissue, the residual heat generated by the current flux lines(typically less than 150° C.), will usually be sufficient to coagulateany severed blood vessels at the site. If not, the surgeon may switchthe power supply 28 into the coagulation mode by lowering the voltage toa level below the threshold for fluid vaporization, as discussed above.This simultaneous hemostasis results in less bleeding and facilitatesthe surgeon's ability to perform the procedure.

Another advantage of the present invention is the ability to preciselyablate soft tissue without causing necrosis or thermal damage to theunderlying and surrounding tissues, nerves or bone. In addition, thevoltage can be controlled so that the energy directed to the target siteis insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise affecting significant damage to the lamina.

Referring now to FIGS. 14 and 15, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to ablate with precision the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the electrode terminals 104 andthe return electrode 112 to elevate the tissue temperature from normalbody temperatures (e.g., 37° C.) to temperatures in the range of 45° C.to 90° C., preferably in the range from 60° C. to 70° C. Thistemperature elevation causes contraction of the collagen connectivefibers within the disc tissue so that the disc 290 withdraws into theannulus 292.

In one method of tissue contraction according to the present invention,an electrically conductive fluid is delivered to the target site asdescribed above, and heated to a sufficient temperature to inducecontraction or shrinkage of the collagen fibers in the target tissue.The electrically conducting fluid is heated to a temperature sufficientto substantially irreversibly contract the collagen fibers, whichgenerally requires a tissue temperature in the range of about 45° C. to90° C., usually about 60° C. to 70° C. The fluid is heated by applyinghigh frequency electrical energy to the electrode terminal(s) in contactwith the electrically conducting fluid. The current emanating from theelectrode terminal(s) 104 heats the fluid and generates a jet or plumeof heated fluid, which is directed towards the target tissue. The heatedfluid elevates the temperature of the collagen sufficiently to causehydrothermal shrinkage of the collagen fibers. The return electrode 112draws the electric current away from the tissue site to limit the depthof penetration of the current into the tissue, thereby inhibitingmolecular dissociation and breakdown of the collagen tissue andminimizing or completely avoiding damage to surrounding and underlyingtissue structures beyond the target tissue site. In an exemplaryembodiment, the electrode terminal(s) 104 are held away from the tissuea sufficient distance such that the RF current does not pass into thetissue at all, but rather passes through the electrically conductingfluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated fluid, ratherthan the electric current.

In an alternate embodiment, the electrode terminal 104 are brought intocontact with, or close proximity to, the target tissue so that theelectric current passes directly into the tissue to a selected depth. Inthis embodiment, the return electrode draws the electric current awayfrom the tissue site to limit its depth of penetration into the tissue.Applicant has discovered that the depth of current penetration also canbe varied with the electrosurgical system of the present invention bychanging the frequency of the voltage applied to the electrode terminaland the return electrode. This is because the electrical impedance oftissue is known to decrease with increasing frequency due to theelectrical properties of cell membranes which surround electricallyconductive cellular fluid. At lower frequencies (e.g., less than 350kHz), the higher tissue impedance, the presence of the return electrodeand the electrode terminal configuration of the present invention(discussed in detail below) cause the current flux lines to penetrateless deeply resulting in a smaller depth of tissue heating. In anexemplary embodiment, an operating frequency of about 100 to 200 kHz isapplied to the electrode terminal(s) to obtain shallow depths ofcollagen shrinkage (e.g., usually less than 1.5 mm and preferably lessthan 0.5 mm).

In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the electrode terminals employed for treatingthe tissue are selected according to the intended depth of tissuetreatment. As described previously in copending patent application PCTInternational Application, U.S. National Phase Ser. No. PCT/US94/05168,the depth of current penetration into tissue increases with increasingdimensions of an individual active electrode (assuming other factorsremain constant, such as the frequency of the electric current, thereturn electrode configuration, etc.). The depth of current penetration(which refers to the depth at which the current density is sufficient toeffect a change in the tissue, such as collagen shrinkage, irreversiblenecrosis, etc.) is on the order of the active electrode diameter for thebipolar configuration of the present invention and operating at afrequency of about 100 kHz to about 200 kHz. Accordingly, forapplications requiring a smaller depth of current penetration, one ormore electrode terminals of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more electrode terminals of larger dimensions wouldbe selected.

FIGS. 16-18 illustrate an alternative electrosurgical system 300specifically configured for endoscopic discectomy procedures, e.g., fortreating extruded or non-extruded herniated discs. As shown in FIG. 16system 300 includes a trocar cannula 302 for introducing a catheterassembly 304 through a percutaneous penetration in the patient to atarget disc in the patient's spine. As discussed above, the catheterassembly 304 may be introduced through the thorax in a thoracoscopicprocedure, through the abdomen in a laparascopic procedure, or directlythrough the patient's back. Catheter assembly 304 includes a catheterbody 306 with a plurality of inner lumens (not shown) and a proximal hub308 for receiving the various instruments that will pass throughcatheter body 306 to the target site. In this embodiment, assembly 304includes an electrosurgical instrument 310 with a flexible shaft 312, anaspiration catheter 314, an endoscope 316 and an illumination fibershaft 318 for viewing the target site. As shown in FIGS. 16 and 17,aspiration catheter 314 includes a distal port 320 and a proximalfigment 322 for attaching catheter 314 to a source of vacuum (notshown). Endoscope 316 will usually comprise a thin metal tube 317 with alens 324 at the distal end, and an eyepiece (not shown) at the proximalend.

In the exemplary embodiment, electrosurgical instrument 310 includes atwist locking stop 330 at a proximal end of the shaft 312 forcontrolling the axial travel distance T_(D) of the probe. As discussedin detail below, this configuration allows the surgeon to “set” thedistance of ablation within the disc. In addition, instrument 310includes a rotational indicator 334 for displaying the rotationalposition of the distal portion of instrument 310 to the surgeon. Thisrotational indicator 334 allows the surgeon to view this rotationalposition without relying on the endoscope 316 if visualization isdifficult, or if an endoscope is not being used in the procedure.

Referring now to FIG. 17, a distal portion 340 of electrosurgicalinstrument 310 and catheter body 306 will now be described. As shown,instrument 310 comprises a relatively stiff, but deflectableelectrically insulating support cannula 312 and a working end portion348 movably coupled to cannula 312 for rotational and translationalmovement of working end 348. Working end 348 of electrosurgicalinstrument 310 can be rotated and translated to ablate and remove avolume of nucleus pulposis within a disc. Support cannula 312 extendsthrough an internal lumen 344 and beyond the distal end 346 of catheterbody 306. Alternatively, support cannula 312 may be separate frominstrument 310, or even an integral part of catheter body 306. Thedistal portion of working end 348 includes an exposed return electrode350 separated from an active electrode array 352 by an insulatingsupport member 354, such as ceramic. In the representative embodiment,electrode array 352 is disposed on only one side of ceramic supportmember 354 so that its other side is insulating and thus atraumatic totissue. Instrument 310 will also include a fluid lumen (not shown)having a distal port 360 in working end 348 for delivering electricallyconductive fluid to the target site.

In use, trocar cannula 302 is introduced into a percutaneous penetrationsuitable for endoscopic delivery to the target disc in the spine. Atrephine (not shown) or other conventional instrument may be used toform a channel from the trocar cannula 302 through the annulus fibrosis370 and into the nucleus pulposis. Alternatively, the probe 310 may beused for this purpose, as discussed above. The working end 348 ofinstrument 310 is then advanced through cannula 302 a short distance(e.g. about 7 to 10 mm) into the nucleus pulposis 372, as shown in FIG.18. Once the electrode array 352 is in position, electrically conductivefluid is delivered through distal port 360 to immerse the activeelectrode array 352 in the fluid. The vacuum source may also beactivated to ensure a flow of conductive fluid between electrode array352 past return electrode 350 to suction port 320, if necessary. In someembodiments, the mechanical stop 330 may then be set at the proximal endof the instrument 310 to limit the axial travel distance of working end348. Preferably, this distance will be set to minimize (or completelyeliminate) ablation of the surrounding annulus.

The probe is then energized by applying high frequency voltagedifference between the electrode array 352 and return electrode 350 sothat electric current flows through the conductive fluid from the array352 to the return electrode 350. The electric current causesvaporization of the fluid and ensuing molecular dissociation of thepulposis tissue as described in detail above. The instrument 310 maythen be translated in an axial direction forwards and backwards to thepreset limits. While still energized and translating, the working end348 may also be rotated to ablate tissue surrounding the electrode array352. In the representative embodiment, working end 348 will also includean inflatable gland 380 opposite electrode array 352 to allow deflectionof working end relative to support cannula 312. As shown in FIG. 18,working end 348 may be deflected to produce a large diameter bore withinthe pulposis, which assures close contact with tissue surfaces to beablated. Alternatively, the entire catheter body 306, or the distal endof catheter body 306 may be deflected to increase the volume of pulposisremoved.

After the desired volume of nucleus pulposis is removed (based on directobservation through port 324, or by kinesthetic feedback from movementof working end 348 of instrument 310), instrument 310 is withdrawn intocatheter body 306 and the catheter body is removed from the patient.Typically, the preferred volume of removed tissue is about 0.2 to 5 cm³.

Referring to FIGS. 19-28, alternative systems and methods for ablatingtissue in confined (e.g., narrow) body spaces will now be described.FIG. 19 illustrates an exemplary planar ablation probe 400 according tothe present invention. Similar to the instruments described above, probe400 can be incorporated into electrosurgical system 11 (or othersuitable systems) for operation in either the bipolar or monopolarmodalities. Probe 400 generally includes a support member 402, a distalworking end 404 attached to the distal end of support member 402 and aproximal handle 408 attached to the proximal end of support member 402.As shown in FIG. 19, handle 406 includes a handpiece 408 and a powersource connector 410 removably coupled to handpiece 408 for electricallyconnecting working end 404 with power supply 28 through cable 34 (seeFIG. 1).

In the embodiment shown in FIG. 19, planar ablation probe 400 isconfigured to operate in the bipolar modality. Accordingly, supportmember 402 functions as the return electrode and comprises anelectrically conducting material, such as titanium, or alloys containingone or more of nickel, chromium, iron, cobalt, copper, aluminum,platinum, molybdenum, tungsten, tantalum or carbon. In the preferredembodiment, support member 402 is an austenitic stainless steel alloy,such as stainless steel Type 304 from MicroGroup, Inc., Medway, Mass. Asshown in FIG. 19, support member 402 is substantially covered by aninsulating layer 412 to prevent electric current from damagingsurrounding tissue. An exposed portion 414 of support member 402functions as the return electrode for probe 400. Exposed portion 414 ispreferably spaced proximally from active electrodes 416 by a distance ofabout 1 to 20 mm.

Referring to FIGS. 20 and 21, planar ablation probe 400 furthercomprises a plurality of active electrodes 416 extending from anelectrically insulating spacer 418 at the distal end of support member402. Of course, it will be recognized that probe 400 may include asingle electrode depending on the size of the target tissue to betreated and the accessibility of the treatment site (see FIG. 26, forexample). Insulating spacer 418 is preferably bonded to support member402 with a suitable epoxy adhesive 419 to form a mechanical bond and afluid-tight seal. Electrodes 416 usually extend about 2.0 mm to 20 mmfrom spacer 418, and preferably less than 10 mm. A support tongue 420extends from the distal end of support member 402 to support activeelectrodes 416. Support tongue 420 and active electrodes 416 have asubstantially low profile to facilitate accessing narrow spaces withinthe patient's body, such as the spaces between adjacent vertebrae andbetween particular cartilage and the meniscus in the patient's knee.Accordingly, tongue 420 and electrodes 416 have a substantially planarprofile, usually having a combined height He of less than 4.0 mm,preferably less than 2.0 mm and more preferably less than 1.0 mm (seeFIG. 25). In the case of ablation of meniscus near particular cartilage,the height He of both the tongue 420 and electrodes 416 is preferablybetween about 0.5 to 1.5 mm. The width of electrodes 416 and supporttongue 420 will usually be less than 10.0 mm and preferably betweenabout 2.0 to 4.0 mm.

Support tongue 420 includes a “non-active” surface 422 opposing activeelectrodes 416 covered with an electrically insulating layer (not shown)to minimize undesirable current flow into adjacent tissue or fluids.Non-active surface 422 is preferably atraumatic, i.e., having a smoothplanar surface with rounded corners, to minimize unwanted injury totissue or nerves in contact therewith, such as disc tissue or the nearbyspinal nerves, as the working end of probe 400 is introduced into anarrow, confined body space. Non-active surface 422 of tongue 420 helpto minimize iatrogenic injuries to tissue and nerves that working end404 of probe 40 can safely access confined spaces within the patient'sbody.

Referring to FIGS. 21 and 22, an electrically insulating support member430 is disposed between support tongue 420 and active electrodes 416 toinhibit or prevent electric current from flowing into tongue 420.Insulating member 430 and insulating layer 412 preferably comprise aceramic, glass or glass ceramic material, such as alumina. Insulatingmember 430 is mechanically bonded to support tongue 420 with a suitableepoxy adhesive to electrically insulate active electrodes 416 fromtongue 420. As shown in FIG. 26, insulating member 430 may overhangsupport tongue 420 to increase the electrical path length between theactive electrodes 416 and the insulation covered support tongue 420.

As shown in FIGS. 21-23, active electrodes 416 are preferablyconstructed from a hollow, round tube, with at least the distal portion432 of electrodes 416 being filed off to form a semi-cylindrical tubewith first and second ends 440, 442 facing away from support tongue 420.Preferably, the proximal portion 434 of electrodes 416 will remaincylindrical to facilitate the formation of a crimp-type electricalconnection between active electrodes 416 and lead wires 450 (see FIG.23). As shown in FIG. 26, cylindrical proximal portions 434 ofelectrodes 416 extend beyond spacer 418 by a slight distance of 0.1 mmto 0.4 mm. The semi-cylindrical configuration of distal electrodeportion 432 increases the electric field intensity and associatedcurrent density around the edges of ends 440, 442, as discussed above.Alternatively, active electrodes 416 may have any of the shapes andconfigurations described above or other configurations, such as squarewires, triangular shaped wires, U-shaped or channel shaped wires and thelike. In addition, the surface of active electrodes 416 may beroughened, e.g., by grit blasting, chemical or electrochemical etching,to further increase the electric field intensity and associated currentdensity around distal portions 432 of electrodes 416.

As shown in FIG. 24, each lead wire 450 terminates at a connector pin452 contained in a pin insulator block 454 within handpiece 408. Leadwires 450 are covered with an insulation layer (not shown), e.g.,Tefzel™, and sealed from the inner portion of support member 402 with anadhesive seal 457 (FIG. 22). In the preferred embodiment, each electrode416 is coupled to a separate source of voltage within power supply 28.To that end, connector pins 452 are removably coupled to matingreceptacles 456 within connector 410 to provide electrical communicationwith active electrodes 416 and power supply 28 (FIG. 1). Electricallyinsulated lead wires 458 connect receptacles 456 to the correspondingsources of voltage within power supply 28. The electrically conductivewall 414 of support member 402 serves as the return electrode, and issuitably coupled to one of the lead wires 450.

In an alternative embodiment, adjacent electrodes 416 may be connectedto the opposite polarity of source 28 so that current flows betweenadjacent active electrodes 416 rather than between active electrodes 416and return electrode 414. By way of example, FIG. 21B illustrates adistal portion of a planar ablation probe 400′ in which electrodes 416 aand 416 c are at one voltage polarity (i.e., positive) and electrodes416 b and 416 d are at the opposite voltage polarity (negative). When ahigh frequency voltage is applied between electrodes 416 a, 416 c andelectrodes 416 b, 416 d in the presence of electrically conductingliquid, current flows between electrodes 416 a, 416 c and 416 b, 416 das illustrated by current flux lines 522′. Similar to the aboveembodiments, the opposite surface 420 of working end 404′ of probe 400′is generally atraumatic and electrically insulated from activeelectrodes 416 a, 416 b, 416 c and 416 d to minimize unwanted injury totissue in contact therewith.

In an exemplary configuration, each source of voltage includes a currentlimiting element or circuitry (not shown) to provide independent currentlimiting based on the impedance between each individual electrode 416and return electrode 414. The current limiting elements may be containedwithin the power supply 28, the lead wires 450, cable 34, handle 406, orwithin portions of the support member 402 distal to handle 406. By wayof example, the current limiting elements may include resistors,capacitors, inductors, or a combination thereof. Alternatively, thecurrent limiting function may be performed by (1) a current sensingcircuit which causes the interruption of current flow if the currentflow to the electrode exceeds a predetermined value and/or (2) animpedance sensing circuit which causes the interruption of current flow(or reduces the applied voltage to zero) if the measured impedance isbelow a predetermined value. In another embodiment, two or more of theelectrodes 416 may be connected to a single lead wire 450 such that allof the electrodes 416 are always at the same applied voltage relative toreturn electrode 414. Accordingly, any current limiting elements orcircuits will modulate the current supplied or the voltage applied tothe array of electrodes 416, rather than limiting their currentindividually, as discussed in the previous embodiment.

Referring to FIGS. 25-28, methods for ablating tissue structures withplanar ablation probe 400 according to the present invention will now bedescribed. In particular, exemplary methods for treating a diseasedmeniscus within the knee (FIGS. 29-31) and for removing soft tissuebetween adjacent vertebrae in the spine (FIG. 32) will be described. Inboth procedures, at least the working end 404 of planar ablation probe400 is introduced to a treatment site either by minimally invasivetechniques or open surgery. Electrically conducting liquid is deliveredto the treatment site, and voltage is applied from power supply 28between active electrodes 416 and return electrode 414. The voltage ispreferably sufficient to generate electric field intensities near activeelectrodes that form a vapor layer in the electrically conductingliquid, and induce the discharge of energy from the vapor layer toablate tissue at the treatment site, as described in detail above.

Referring to FIG. 25, working end 404 and at least the distal portion ofsupport member 402 are introduced through a percutaneous penetration500, such as a cannula, into the arthroscopic cavity 502. The insertionof probe 400 is usually guided by an arthroscope (not shown) whichincludes a light source and a video camera to allow the surgeon toselectively visualize a zone within the knee joint. To maintain a clearfield of view and to facilitate the generation of a vapor layer, atransparent, electrically conductive irrigant 503, such as isotonicsaline, is injected into the treatment site either through a liquidpassage in support member 402 of probe 400, or through anotherinstrument. Suitable methods for delivering irrigant to a treatment siteare described in commonly assigned, co-pending application U.S. Pat. No.5,697,281 filed on Jun. 7, 1995, previously incorporated herein byreference.

In the example shown in FIG. 25, the target tissue is a portion of themeniscus 506 adjacent to and in close proximity with the particularcartilage 510, 508 which normally covers the end surfaces of the tibia512 and the femur 514, respectively. The particular cartilage 508, 510is important to the normal functioning of joints, and once damaged, thebody is generally not capable of regenerating this critical lining ofthe joints. Consequently, it is desirable that the surgeon exerciseextreme care when treating the nearby meniscus 506 to avoid unwanteddamage to the particular cartilage 508, 510. The confined spaces 513between particular cartilage 508, 510 and meniscus 506 within the kneejoint are relatively narrow, typically on the order of about 1.0 mm to5.0 mm. Accordingly, the narrow, low profile working end 404 of ablationprobe 400 is ideally suited for introduction into these confined spaces513 to the treatment site. As mentioned previously, the substantiallyplanar arrangement of electrodes 416 and support tongue 420 (typicallyhaving a combined height of about 0.5 to 1.5 mm) allows the surgeon todeliver working end 404 of probe 400 into the confined spaces 513, whileminimizing contact with the particular cartilage 508, 510 (see FIG. 26).

As shown in FIG. 26, active electrodes 416 are disposed on one face ofworking end 404 of probe 400. Accordingly, a zone 520 of high electricfield intensity is generated on each electrode 416 on one face ofworking end 404 while the opposite side 521 of working end 404 isatraumatic with respect to tissue. In addition, the opposite side 521 isinsulated from electrodes 416 to minimize electric current from passingthrough this side 521 to the tissue (i.e., adjacent particular cartilage508). As shown in FIGS. 26, the bipolar arrangement of active electrodes416 and return electrode 414 causes electric current to flow along fluxlines 522 predominantly through the electrically conducting irrigant503, which envelops the tissue and working end 404 of ablation probe 400and provides an electrically conducting path between electrodes 416 andreturn electrode 414. As electrodes 416 are engaged with, or positionedin close proximity to, the target meniscus 506, the high electric fieldpresent at the electrode edges cause controlled ablation of the tissueby forming a vapor layer and inducing the discharge of energy therefrom.In addition, the motion of electrodes 416 relative to the meniscus 506(as shown by vector 523) causes tissue to be removed in a controlledmanner. The presence of the irrigant also serves to minimize theincrease in the temperature of the meniscus during the ablation processbecause the irrigant generally comes in contact with the treated tissueshortly after one of the electrodes 416 has been translated across thesurface of the tissue.

Referring now to FIG. 28, an exemplary method for removing soft tissue540 from the surfaces of adjacent vertebrae 542, 544 in the spine willnow be described. Removal of this soft tissue 540 is often necessary,for example, in surgical procedures for fusing or joining adjacentvertebrae together. Following the removal of tissue 540, the adjacentvertebrae 542, 544 are stabilized to allow for subsequent fusiontogether to form a single monolithic vertebra. As shown, the low-profileof working end 404 of probe 400 (i.e., thickness values as low as 0.2mm) allows access to and surface preparation of closely spacedvertebrae. In addition, the shaped electrodes 416 promote substantiallyhigh electric field intensities and associated current densities betweenactive electrodes 416 and return electrode 414 to allow for theefficient removal of tissue attached to the surface of bone withoutsignificantly damaging the underlying bone. The “non-active” insulatingside 521 of working end 404 also minimizes the generation of electricfields on this side 521 to reduce ablation of the adjacent vertebra 542.

The target tissue is generally not completely immersed in electricallyconductive liquid during surgical procedures within the spine, such asthe removal of soft tissue described above. Accordingly, electricallyconducting liquid will preferably be delivered into the confined spaces513 between adjacent vertebrae 542, 544 during this procedure. The fluidmay be delivered through a liquid passage (not shown) within supportmember 402 of probe 400, or through another suitable liquid supplyinstrument.

Other modifications and variations can be made to disclose embodimentswithout departing from the subject invention as defined in the followingclaims. For example, it should be clearly understood that the planarablation probe 400 described above may incorporate a single activeelectrode, rather than a plurality of such active electrodes asdescribed above in the exemplary embodiment. FIG. 27 illustrates aportion of a planar ablation probe according to the present inventionthat incorporates a single active electrode 416′ for generating highelectric field densities 550 to ablate a target tissue 552. Electrode416′ may extend directly from a proximal support member, as depicted inFIG. 31, or it may be supported on an underlying support tongue (notshown) as described in the previous embodiment. As shown, therepresentative single active electrode 416′ has a semi-cylindricalcross-section, similar to the electrodes 416 described above. However,the single electrode 416′ may also incorporate any of the abovedescribed configurations (e.g., square or star shaped solid wire) orother specialized configurations depending on the function of thedevice.

Referring now to FIGS. 29-31 an alternative electrode support member 500for a planar ablation probe 404 will be described in detail. As shown,electrode support member 500 preferably comprises a multilayer or singlelayer substrate 502 comprising a suitable high temperature, electricallyinsulating material, such as ceramic. The substrate 502 is a thin orthick film hybrid having conductive strips that are adhered to, e.g.,plated onto, the ceramic wafer. The conductive strips typically comprisetungsten, gold, nickel or equivalent materials. In the exemplaryembodiment, the conductive strips comprise tungsten, and they areco-fired together with the wafer layers to form an integral package. Theconductive strips are coupled to external wire connectors by holes orvias that are drilled through the ceramic layers, and plated orotherwise covered with conductive material.

In the representative embodiment, support member 500 comprises a singleceramic wafer having a plurality of longitudinal ridges 504 formed onone side of the wafer 502. Typically, the wafer 502 is green pressed andfired to form the required topography (e.g., ridges 504). A conductivematerial is then adhered to the ridges 502 to form conductive strips 506extending axially over wafer 502 and spaced from each other. As shown inFIG. 30, the conductive strips 506 are attached to lead wires 508 withinshaft 412 of the probe 404 to electrically couple conductive strips 506with the power supply 28 (FIG. 1). This embodiment provides a relativelylow profile working end of probe 404 that has sufficient mechanicalstructure to withstand bending forces during the procedure.

FIGS. 34-36 illustrate another system and method for treating swollen orherniated spinal discs according to the present invention. In thisprocedure, an electrosurgical probe 700 comprises a long, thin shaft 702(e.g., on the order of about 1 mm in diameter or less) that can bepercutaneously introduced anteriorly through the abdomen or thorax, orthrough the patient's back directly into the spine. The probe shaft 702will include one or more active electrode(s) 704 for applying electricalenergy to tissues within the spine. The probe 700 may include one ormore return electrode(s) 706, or the return electrode may be positionedon the patient's back, as a dispersive pad (not shown).

As shown in FIG. 34, the distal portion of shaft 702 is introducedanteriorly through a small percutaneous penetration into the annulus 710of the target spinal disc. To facilitate this process, the distal end ofshaft 702 may taper down to a sharper point (e.g., a needle), which canthen be retracted to expose active electrode(s) 704. Alternatively, theelectrodes may be formed around the surface of the tapered distalportion of shaft (not shown). In either embodiment, the distal end ofshaft is delivered through the annulus 710 to the target nucleuspulposis 290, which may be herniated, extruded, non-extruded, or simplyswollen. As shown in FIG. 35, high frequency voltage is applied betweenactive electrode(s) 704 and return electrode(s) 710 to heat thesurrounding collagen to suitable temperatures for contraction (i.e.,typically about 55° C. to about 70° C.). As discussed above, thisprocedure may be accomplished with a monopolar configuration, as well.However, applicant has found that the bipolar configuration shown inFIGS. 34-36 provides enhanced control of the high frequency current,which reduces the risk of spinal nerve damage.

As shown in FIG. 35 and 36, once the pulposis 290 has been sufficientcontracted to retract from impingement on the nerve 720, the probe 700is removed from the target site. In the representative embodiment, thehigh frequency voltage is applied between active and return electrode(s)704 706 as the probe is withdrawn through the annulus 710. This voltageis sufficient to cause contraction of the collagen fibers within theannulus 710, which allows the annulus 710 to contract around the holeformed by probe 700, thereby improving the healing of this hole. Thus,the probe 700 seals its own passage as it is withdrawn from the disc.

Other modifications and variations can be made to disclose embodimentswithout departing from the subject invention as defined in the followingclaims. For example, it should be noted that the invention is notlimited to an electrode array comprising a plurality of electrodeterminals. The invention could utilize a plurality of return electrodes,e.g., in a bipolar array or the like. In addition, depending on otherconditions, such as the peak-to-peak voltage, electrode diameter, etc.,a single electrode terminal may be sufficient to contract collagentissue, ablate tissue, or the like.

In addition, the active and return electrodes may both be located on adistal tissue treatment surface adjacent to each other. The active andreturn electrodes may be located in active/return electrode pairs, orone or more return electrodes may be located on the distal tip togetherwith a plurality of electrically isolated electrode terminals. Theproximal return electrode may or may not be employed in theseembodiments. For example, if it is desired to maintain the current fluxlines around the distal tip of the probe, the proximal return electrodewill not be desired.

What is claimed is:
 1. An electrosurgical apparatus for treating tissuewithin a patient's spine comprising: a shaft having a proximal endportion and a distal end portion sized to fit within an intervertebraldisc in the patient's spine; an electrode terminal on the distal endportion of the shaft; a return electrode; an insulating memberpositioned between the return electrode and the electrode terminal, thereturn electrode being sufficiently spaced from the electrode terminalto minimize direct contact between the return electrode and a bodystructure in or on the disc when the electrode terminal is positioned inclose proximity or in partial contact with the body structure; and meansfor applying a high frequency voltage difference between the electrodeterminal and the return electrode to reduce a volume of the disc torelieve pressure on a spinal nerve.
 2. The apparatus of claim 1 furthercomprising means for applying sufficient high frequency voltage betweenthe electrode terminal and the return electrode to ablate a portion ofthe nucleus pulposis within the disc.
 3. The apparatus of claim 1further comprising means for applying sufficient high frequency voltagebetween the electrode terminal and the return electrode to contractcollagen fibers within the nucleus pulposis within the disc.
 4. Theapparatus of claim 1 further comprising a fluid delivery elementdefining a fluid path in electrical contact with the return electrodeand the electrode terminal to generate a current flow path between thereturn electrode and the electrode terminal.
 5. The apparatus of claim 4wherein the fluid delivery element comprises a fluid tube extendingalong an outer surface of the shaft, the tube having an inlet positionedproximal to the return electrode, wherein the return electrode is spacedproximally from the electrode terminal.
 6. The apparatus of claim 4wherein the fluid delivery element comprises a fluid supply instrumentseparate from the shaft.
 7. The apparatus of claim 1 wherein the distalend portion of the shaft has a diameter less than about 2.0 mm.
 8. Theapparatus of claim 1 wherein the return electrode forms a portion of theshaft.
 9. The apparatus of claim 1 wherein the electrode terminalcomprises an electrode array disposed near the distal end portion of theshaft, the array including a plurality of electrically isolatedelectrode terminals disposed over a contact surface.
 10. The apparatusof claim 1 wherein the electrode terminal comprises a single activeelectrode disposed near the distal end portion of the shaft.
 11. Theapparatus of claim 1 further comprising a fluid aspiration element foraspirating fluid from a region around the electrode terminal.
 12. Theapparatus of claim 11 wherein the fluid aspiration element comprises asuction lumen extending through the shaft, the suction lumen having aninlet at a distal tip of the shaft adjacent the electrode terminal. 13.The apparatus of claim 12 further comprising an aspiration electrode ator near the inlet of the suction lumen for ablating tissue fragmentsaspirated into the suction lumen.
 14. The apparatus of claim 13 whereinthe aspiration electrode comprises a mesh electrode having one or moreopenings positioned across the inlet of the suction lumen.
 15. Theapparatus of claim 14 wherein the mesh electrode and the electrodeterminal are electrically coupled to each other to form a singleelectrode.
 16. The apparatus of claim 14 wherein the mesh electrodecomprises a material having a different voltage potential than theelectrode terminal.
 17. The apparatus of claim 1 wherein the distal endportion of the shaft has an active side and a substantially planarnon-active side opposing the active side, the electrode terminal beingdisposed on the active side and being insulated from the non-activeside.
 18. The apparatus of claim 17 wherein the distal end portion ofthe shaft has a thickness from the active side to the non-active side ofless than 2 mm.
 19. The apparatus of claim 1 further comprising anelectrically insulating support member extending from the distal endportion of the shaft, the electrode terminal being mounted to thesupport member.
 20. The apparatus of claim 19 wherein the support memberis an insulating wafer having a tissue treatment surface disposed at ornear the distal end portion of the shaft, the insulating wafer having atleast one conductive strip forming the electrode terminal, the apparatusfurther comprising an electrical connector extending from the conductivestrip to the proximal end portion of the shaft for coupling theelectrode terminal to the applying means.
 21. The apparatus of claim 20further comprising a plurality of conductive strips on the insulatingwafer forming an array of electrically isolated terminals on the tissuetreatment surface.
 22. The apparatus of claim 21 wherein the conductivestrips are substantially linear and parallel to each other, the waferincluding a plurality of ridges extending from the tissue treatmentsurface, and the conductive strips being formed on the ridges.
 23. Theapparatus of claim 20 wherein the insulating wafer comprises ceramic andthe conductive strip comprises tungsten.
 24. An electrosurgicalapparatus for treating tissue within a patient's spine comprising: ashaft having a proximal end portion and a distal end portion sized tofit within an intervertebral disc in the patient's spine; an electrodeterminal on the distal end portion of the shaft; a return electrode; afluid delivery element defining a fluid path in electrical contact withthe return electrode and the electrode terminal to generate a currentflow path between the return electrode and the electrode terminal,wherein the fluid delivery element comprises a fluid tube extending along an outer surface of the shaft, the tube having an inlet positionedproximal to the return electrode, wherein the return electrode is spacedproximally from the electrode terminal; and means for applying a highfrequency voltage difference between the electrode terminal and thereturn electrode to reduce a volume of the disc to relieve pressure on aspinal nerve.
 25. The apparatus of claim 24 further comprising means forapplying sufficient high frequency voltage between the electrodeterminal and the return electrode to ablate a portion of the nucleuspulposis within the disc.
 26. The apparatus of claim 24 furthercomprising means for applying sufficient high frequency voltage betweenthe electrode terminal and the return electrode to contract collagenfibers within the nucleus pulposis within the disc.
 27. The apparatus ofclaim 24 wherein the distal end portion of the shaft has a diameter lessthan about 2.0 mm.
 28. The apparatus of claim 24 wherein the returnelectrode forms a portion of the shaft.
 29. The apparatus of claim 24further including an insulating member positioned between the returnelectrode and the electrode terminal, the return electrode beingsufficiently spaced from the electrode terminal to minimize directcontact between the return electrode and a body structure on or in thedisc when the electrode terminal is positioned in close proximity or inpartial contact with the body structure.
 30. The apparatus of claim 24wherein the electrode terminal comprises an electrode array disposednear the distal end portion of the shaft, the array including aplurality of electrically isolated electrode terminals disposed over acontact surface.
 31. The apparatus of claim 24 wherein the electrodeterminal comprises a single active electrode disposed near the distalend portion of the shaft.
 32. The apparatus of claim 24 furthercomprising a fluid aspiration element for aspirating fluid from a regionaround the electrode terminal.
 33. The apparatus of claim 32 wherein thefluid aspiration element comprises a suction lumen extending through theshaft, the suction lumen having an inlet at a distal tip of the shaftadjacent the electrode terminal.
 34. The apparatus of claim 32 furthercomprising an aspiration electrode at or near the inlet of the suctionlumen for ablating tissue fragments aspirated into the suction lumen.35. The apparatus of claim 34 wherein the aspiration electrode comprisesa mesh electrode having one or more openings positioned across the inletof the suction lumen.
 36. The apparatus of claim 35 wherein the meshelectrode and the electrode terminal are electrically coupled to eachother to form a single electrode.
 37. The apparatus of claim 35 whereinthe mesh electrode comprises a material having a different voltagepotential than the electrode terminal.